Concrete is a versatile building material made by mixing cement, aggregate, and water in a proper proportion. Traditionally, the water is introduced in liquid phase and the concrete is cured in a moist condition for twenty-eight days to reach a design strength. See "Design and Control of Concrete Mixtures", Twelfth edition, Portland Cement Association, ISNBN 0-89312-023-5 at page 11 (1979). This procedure has been used for centuries and is still the dominant technology in concrete construction around the world today.
More recently, some manufacturers of precast concrete have reported mixing cement, aggregate, and liquid water to produce a wet mixture and, subsequently, contacting the wet mixture with steam in order to accelerate a curing process. In some cases, steaming of the wet mixture is reportedly followed by a relatively longer period of natural curing, which is said to produce a concrete which develops a useful design strength in a relatively short time.
It has been published that a mortar made from Portland cement and fine (virgin) aggregate exhibits a relatively high compressive strength when cured by contact with steam at greater than atmospheric pressure. For example, Republic of China (Taiwan) Patent No. 55,148 describes autoclaving a dry cement and sand mixture in the presence of steam for time periods in the range of 6 to 18 hours. Mortar cubes having desirably high compressive strengths are also described in that patent.
However, many industrial nations are currently in need of a practical method for recycling waste materials, particularly construction debris known as rubble. To date, concrete mixtures containing rubble are not commonly employed as building materials. Concrete containing recycled materials often exhibits relatively poor compressive strength, apparently as a result of weaker bond strengths at interfaces between cement paste and recycled materials used as aggregate.
Accordingly, a need exists for a method for producing stronger concrete from mixtures containing recycled materials. Similarly, a method for producing stronger concrete products, generally, from Portland cement and aggregate would be enthusiastically received by the construction community.